Methylene bis(cyclohexylamine)-initiated polyols and rigid polyurethane foam made therefrom

ABSTRACT

Polyether polyols are initiated with methylene bis(cyclohexylamines). The polyols are useful in making rigid polyurethane foams, especially foams for pour-in-place applications, where they give a good combination of low k-factor and short demold times.

This application claims priority from U.S. Provisional PatentApplication No. 61/060,236, filed 10 Jun. 2008.

This invention pertains to polyols that are useful for manufacturingrigid polyurethane foams, as well as rigid foams made from thosepolyols.

Rigid polyurethane foams have been used widely for several decades asinsulation foam in appliances and other applications, as well as avariety of other uses. These foams are prepared in a reaction of apolyisocyanate and one or more polyol, polyamine or aminoalcoholcompounds. The polyol, polyamine or aminoalcohols compounds can becharacterized as having equivalent weights per isocyanate-reactive groupin the range of up to about 300 and an average of more than threehydroxyl and/or amino groups per molecule. The reaction is conducted inthe presence of a blowing agent which generates a gas as the reactionproceeds. The gas expands the reacting mixture and imparts a cellularstructure.

Originally, the blowing agent of choice was a “hard” chlorofluorocarbon(CFC) such as trichlorofluoromethane or dichlorodifluoromethane. TheseCFCs processed very easily and produced foam having very good thermalinsulation properties. However, the CFC blowing agents have been phasedout because of environmental concerns.

CFCs have been replaced with other blowing agents such ashydrofluorocarbons, low-boiling hydrocarbons, hydrochlorofluorocarbons,ether compounds, and water (which reacts with isocyanates to generatecarbon dioxide). For the most part, these alternative blowing agents areless effective thermal insulators than their CFC predecessors. Theability of a foam to provide thermal insulation is often expressed interms of “k-factor”, which is a measure of the amount of heat that istransferred through the foam per unit area per unit time, taking intoaccount the thickness of the foam and the applied temperature differenceacross the foam thickness. Foams produced using alternative blowingagents tend to have higher k-factors than those produced using “hard”CFC blowing agents. This has forced rigid foam producers to modify theirfoam formulations in other ways to compensate for the loss of thermalinsulation values that result from the changes in blowing agent. Many ofthese modifications focus on reducing cell size in the foam.Smaller-sized cells tend to provide better thermal insulationproperties.

It has been found that modifications to a rigid foam formulation whichimprove k-factor tend to affect the processing characteristics of theformulation in an undesirable way. The curing characteristics of theformulation are important, especially in pour-in-place applications suchas appliance foam. Refrigerator and freezer cabinets, for example, areusually insulated by partially assembling an exterior shell and interiorliner, and holding them in position such that a cavity is formed betweenthem. The foam formulation is introduced into the cavity, where itexpands to fill the cavity. The foam provides thermal insulation andimparts structural strength to the assembly. The way the foamformulation cures is important in at least two respects. First, the foamformulation must cure quickly to form a dimensionally stable foam, sothat the finished cabinet can be removed from the jig. Thischaracteristic is generally referred to as “demold” time, and directlyaffects the rate at which cabinets can be produced.

In addition, the curing characteristics of the system affect a propertyknown as “flow index” or simply “flow”. A foam formulation will expandto a certain density (known as the ‘free rise density’) if permitted toexpand against minimal constraints. When the formulation must fill arefrigerator or freezer cabinet, its expansion is somewhat constrainedin several ways. The foam must expand mainly in a vertical (rather thanhorizontal) direction within a narrow cavity. As a result, theformulation must expand against a significant amount of its own weight.The foam formulation also must flow around corners and into all portionsof the wall cavities. In addition, the cavity often has limited or noventing, and so the atmosphere in the cavity exerts additional pressureon the expanding foam. Because of these constraints, a greater amount ofthe foam formulation is needed to fill the cavity than would bepredicted from the free rise density alone. The amount of foamformulation needed to minimally fill the cavity can be expressed as aminimum fill density (the weight of the formulation divided by thecavity volume). The ratio of the minimum fill density to the free risedensity is the flow index. The flow index is ideally 1.0, but is on theorder of 1.2 to 1.8 in commercially practical formulations. Lower flowindex is preferred, all other things being equal, because raw materialscosts are lower when a smaller weight of foam is needed.

Modifications to foam formulations that favor low k-factor tend to havean adverse effect on demold time, flow index or both. Therefore,although formulations have been developed which closely matchconventional CFC-based formulations in k-factor, the overall cost ofusing these formulations is often higher due to lower productivity(because of greater demold times), higher raw materials costs (becauseof higher flow index) or both.

What is desired is a rigid foam formulation that provides a low k-factorfoam with a low flow index and a short demold time.

This invention is in one aspect an amine-initiated polyol having anaverage hydroxyl functionality of greater than 3.0 to 4.0, theamine-initiated polyol being a reaction product of at least one C₂-C₄alkylene oxide with a methylene bis(cyclohexylamine) initiator compound.

The invention is also a process for preparing a rigid polyurethane foam,comprising

-   a) forming a reactive mixture containing at least-   1) an amine-initiated polyol according having an average hydroxyl    functionality of greater than 3.0 to 4.0 and a hydroxyl equivalent    weight of from 75 to 560, the amine-initiated polyol being a    reaction product of at least one C₂-C₄ alkylene oxide with a    methylene bis(cyclohexylamine) initiator compound, or mixture of the    amine-initiated polyol with at least one other polyol, provided that    such a mixture contains at least 5% by weight of the amine-initiated    polyol;-   2) at least one hydrocarbon, hydrofluorocarbon,    hydrochlorofluorocarbon, fluorocarbon, dialkyl ether or    fluorine-substituted dialkyl ether physical blowing agent; and-   3) at least one polyisocyanate; and-   b) subjecting the reactive mixture to conditions such that the    reactive mixture expands and cures to form a rigid polyurethane    foam.

In another aspect, the invention is a rigid foam made in accordance withthe foregoing process.

It has been found that rigid foam formulations that include themethylene bis(cyclohexylamine-initiated) polyol often exhibit desirablecuring characteristics (as indicated by flow index of below 1.8) andshort demold times, and cure to form a foam having excellent thermalinsulation properties (i.e., low k-factor). These advantages are seenparticularly when the methylene bis(cyclohexylamine)-initiated polyol isused in admixture with one or more other polyols that have a hydroxylfunctionality of from 4 to 8 and a hydroxyl equivalent weight from 75 to200.

The amine-initiated polyol is a polyether that is prepared from at leastone methylene bis(cyclohexylamine) initiator compound. A “methylenebis(cyclohexylamine)” initiator compound, for purposes of thisinvention, is a compound that contains a methylene group which issubstituted with two cyclohexylamine groups, which may contain furthersubstituents as described more fully below. A “methylenebis(cyclohexylamine)-initiated polyol” is, for purposes of thisinvention, a polyol prepared by reacting a methylenebis(cyclohexylamine) initiator, as so defined, with at least one C₂-C₄alkylene oxide. The cyclohexyl groups may be unsubstituted or inertlysubstituted. The “methylene bis(cyclohexylamine)” initiator compound canbe represented by the structure:

wherein each R is hydrogen or an inert substituent. The NH₂ groups maybe in the 2, 3 or 4 positions. The two NH₂ groups may be symmetricallyor asymmetrically positioned with respect to the central methylenegroup. Preferred isomers are the 2,2′, 4,4′ and 2,4′ isomers.

Each R is preferably hydrogen, but any one or more of the R groups maybe an inert substitutent. An “inert” substituent is one that (1) is notreactive with an alkylene oxide under the conditions of alkoxylation (asdescribed more below), (2) is not reactive with isocyanate groups and(3) does not significantly affect the ability of the methylenebis(cyclohexylamine) compound to become alkoxylated and of the resultingpolyol to react with a polyisocyanate to form urethane linkages. Inertsubstituents include hydrocarbyl groups such as alkyl, alkenyl, alkynyl,aryl, aryl-substituted alkyl, cycloalkyl and the like; ether groups;tertiary amino groups; and the like. It is preferred that anysubstituent groups R that may be present are C₁-C₄ alkyl. Among theseare methyl, propyl, isopropyl, n-butyl, and isobutyl groups, with methylbeing preferred among these. If an inert substitutent group is present,it is preferred to have no more than one such group per cyclohexanering. Most preferably, all R groups are hydrogen, and the compound isunsubstituted.

Some specific methylene bis(cyclohexylamine) initiators includemethylene bis(4-aminocyclohexane), methylene bis(2-aminocyclohexane),2,4′-diamino-methylene bis(cyclohexane), methylenebis(4-amino-2-methyl-cyclohexane), methylenebis(2-amino-4-methyl-cyclohexane), methylenebis(4-amino-3-methyl-cyclohexane) (commercially available as Laromin® C260) and the like. The foregoing nomenclature takes designates thecyclohexane carbon atom bonded to the methylene group as the “1”position.

The methylene bis(cyclohexylamine) compounds usually exist in two ormore diastereoisomeric forms. In such cases, any of thediastereoisomeric forms, or mixtures of any two or more of thediastereoisomeric forms, can be used.

In addition, mixtures of two or methylene bis(cyclohexylamine) compoundsas just described can be used.

The methylene bis(cyclohexylamine) compound may contain small amounts(typically less than 3% by weight) of impurities, which tend to bemainly other amine or diamine compounds. Methylene bis(cyclohexylamine)compounds containing such small levels of these impurities are suitableas initiators in the present invention.

The initiator compound is caused to react with at least one C₂-C₄alkylene oxide to produce the amine-initiated polyol. The alkylene oxidemay be ethylene oxide, 1,2-propylene oxide, 1,2- or 2,3-butylene oxide,tetramethylene oxide or a combination of two or more thereof. If two ormore alkylene oxides are used, they may be added to the initiatorcompound simultaneously (to form a random copolymer) or sequentially (toform a block copolymer). Butylene oxide and tetramethylene oxide aregenerally less preferred. Ethylene oxide, propylene oxide and mixturesthereof are more preferred. Mixtures of ethylene oxide and propyleneoxide may contain the oxides in any proportion. For example, a mixtureof ethylene oxide and propylene oxide may contain from 10 to 90 weightpercent of ethylene oxide, preferably from 30 to 70 weight percentethylene oxide or from 40 to 60 weight percent ethylene oxide.

Enough of the alkylene oxide(s) are added to the initiator to produce apolyol having an average hydroxyl functionality of greater than 3.0, upto as many as 4.0, hydroxyl groups/molecule. A preferred averagehydroxyl functionality for the polyol is from 3.3 to 4.0, and a morepreferred average hydroxyl functionality is from 3.7 to 4.0. A methylenebis(cyclohexylamine)-initiated polyol that is useful for preparing rigidpolyurethane foam suitably has a hydroxyl equivalent weight of from 75to 560. A preferred hydroxyl equivalent weight for rigid foam productionis from 90 to 175 and a more preferred hydroxyl equivalent weight forrigid foam production is from 100 to 130.

The alkoxylation reaction is conveniently performed by forming a mixtureof the alkylene oxide(s) and the initiator compound, and subjecting themixture to conditions of elevated temperature and superatmosphericpressure. Polymerization temperatures may be, for example, from 110 to170° C., and pressures may be, for example, from 2 to 10 bar (200 to1000 kPa). A catalyst may be used, particularly if more than one mole ofalkylene oxide(s) is to be added per equivalent of amine hydrogen on theinitiator compound. Suitable alkoxylation catalysts include strong basessuch as alkali metal hydroxides (sodium hydroxide, potassium hydroxide,cesium hydroxide, for example), as well as the so-called double metalcyanide catalysts (of which zinc hexacyanocobaltate complexes are mostnotable). The reaction can be performed in two or more stages, in whichno catalyst is used in the first stage, and from 0.5 to 1.0 mole ofalkylene oxide is added to the initiator per equivalent of aminehydrogens, followed by one or more subsequent stages in which additionalalkylene oxide is added in the presence of a catalyst as described.After the reaction is completed, the catalyst may be deactivated and/orremoved. Alkali metal hydroxide catalysts may be removed, left in theproduct, or neutralized with an acid and the residues left in theproduct. Residues of double metal cyanide catalysts may be left in theproduct, but can be removed instead if desired.

The preferred amine-initiated polyol is a reaction product of methylenebis(4-aminocyclohexane), methylene bis(2-aminocyclohexane),2,4′-diamino-methylene bis(cyclohexane), methylenebis(4-amino-2-methyl-cyclohexane), methylenebis(2-amino-4-methyl-cyclohexane) or methylenebis(4-amino-3-methyl-cyclohexane) (or mixture of two or more of thoseisomers) with a mixture of from 30 to 70 mole percent ethylene oxide and70 to 30 mole percent propylene oxide, having a hydroxyl functionalityof from 3.3 to 4.0, especially 3.7 to 4.0, and a hydroxyl equivalentweight of from 90 to 175, especially from 100 to 130.

The amine-initiated polyol is useful in preparing rigid polyurethanefoam, particularly when its hydroxyl equivalent weight is from 75 to560. The rigid polyurethane foam is prepared from a polyurethane-formingcomposition that contains at least (1) the amine-initiated polyol,optionally in combination with one or more other polyols, (2) at leastone organic polyisocyanate, and (3) at least one physical blowing agentas described more fully below.

The methylene bis(cyclohexylamine)-initiated polyol suitably constitutesat least 5 weight percent of all polyols present in thepolyurethane-forming composition. Below this level, the benefits ofusing the polyol are slight. The methylenebis(cyclohexylamine)-initiated polyol may be the sole polyol in thepolyurethane-forming composition. However, it is anticipated that inmost cases it will be used in a mixture containing at least one otherpolyol, and that the methylene bis(cyclohexylamine)-initiated polyolwill constitute from about 5 to about 75% of the combined weight of allthe polyols. For example, the methylene bis(cyclohexylamine)-initiatedpolyol may constitute from 10 to about 60% of the combined weight of allthe polyols, or from about 10 to about 50% of the combined weight of allthe polyols.

When a mixture of polyols is used, the polyol mixture preferably has anaverage of 3.5 to about 7 hydroxyl groups/molecule and an averagehydroxyl equivalent weight of about 90 to about 175. Any individualpolyol within the mixture may have a functionality and/or equivalentweight outside of those ranges, if the mixture meets these parameters.Water is not considered in determining the functionality or equivalentweight of a polyol mixture.

A more preferred average hydroxyl functionality for a polyol mixture isfrom about 3.8 to about 6 hydroxyl groups/molecule. An even morepreferred average hydroxyl functionality for a polyol mixture is fromabout 3.8 to about 5 hydroxyl groups/molecule. A more preferred averagehydroxyl equivalent weight for a polyol mixture is from about 110 toabout 130.

Suitable polyols that can be used in conjunction with the methylenebis(cyclohexylamine)-initiated polyol include polyether polyols, whichare conveniently made by polymerizing an alkylene oxide onto aninitiator compound (or mixture of initiator compounds) that has multipleactive hydrogen atoms. The initiator compound(s) may include alkyleneglycols (e.g., ethylene glycol, propylene glycol, 1,4-butane diol,1,6-hexanediol and the like), glycol ethers (such as diethylene glycol,triethylene glycol, dipropylene glycol, tripropylene glycol and thelike), glycerine, trimethylolpropane, pentaerythritol, sorbitol,sucrose, glucose, fructose or other sugars, and the like. A portion ofthe initiator compound may be one containing primary and/or secondaryamino groups, such as ethylene diamine, hexamethylene diamine,diethanolamine, monoethanolamine, N-methyldiethanolamine, piperazine,aminoethylpiperazine, diisopropanolamine, monoisopropanolamine,methanolamine, dimethanolamine, toluene diamine (all isomers) and thelike. Amine-initiated polyols of these types tend to be somewhatautocatalytic. The alkylene oxide used to make the additional polyol(s)are as described before with respect to the methylenebis(cyclohexylamine)-initiated polyol. The alkylene oxide of choice ispropylene oxide, or a mixture of propylene oxide and ethylene oxide.

Polyester polyols may also be used as an additional polyol, but aregenerally less preferred as they tend to have lower functionalities. Thepolyester polyols include reaction products of polyols, preferablydiols, with polycarboxylic acids or their anhydrides, preferablydicarboxylic acids or dicarboxylic acid anhydrides. The polycarboxylicacids or anhydrides may be aliphatic, cycloaliphatic, aromatic and/orheterocyclic and may be substituted, such as with halogen atoms. Thepolycarboxylic acids may be unsaturated. Examples of thesepolycarboxylic acids include succinic acid, adipic acid, terephthalicacid, isophthalic acid, trimellitic anhydride, phthalic anhydride,maleic acid, maleic acid anhydride and fumaric acid. The polyols used inmaking the polyester polyols include ethylene glycol, 1,2- and1,3-propylene glycol, 1,4- and 2,3-butane diol, 1,6-hexane diol,1,8-octane diol, neopentyl glycol, cyclohexane dimethanol,2-methyl-1,3-propane diol, glycerine, trimethylol propane, 1,2,6-hexanetriol, 1,2,4-butane triol, trimethylol ethane, pentaerythritol,quinitol, mannitol, sorbitol, methyl glycoside, diethylene glycol,triethylene glycol, tetraethylene glycol, dipropylene glycol, dibutyleneglycol and the like.

In some embodiments of the invention, the methylenebis(cyclohexylamine)-initiated polyol used present in a polyol mixturethat contains at least one renewable-resource polyol having from 2 to 6hydroxyl groups per molecule and a hydroxyl equivalent weight of from 75to 1000. The renewable-resource polyol in those embodiments constitutesat least 1% by weight of the polyol mixture, and preferably constitutesfrom 1 to 15% weight percent thereof.

A “renewable-resource polyol”, for purposes of this invention, is apolyol that is, or is produced from, a renewable biological resource,such as an animal fat, a vegetable fat, a lignocellulosic material or acarbohydrate such as starch. At least 50% of the mass of therenewable-resource polyol should come from the renewable biologicalresource. Various types of renewable-resource polyols are useful,including those described in Ionescu, Chemistry and Technology ofPolyols for Polyurethanes, Rapra Publishers 2005. These include

1. Castor oil;

2. A hydroxymethyl group-containing polyol as described in WO2004/096882 and WO 2004/096883. Such polyols are prepared by reacting ahydroxymethyl group-containing fatty acid having from 12-26 carbonatoms, or an ester of such a hydroxymethyl group containing fatty acid,with a polyol or polyamine initiator compound having an average of atleast 2 hydroxyl, primary amine and/or secondary amine groups, such thatthe hydroxymethyl-containing polyester polyol contains an average of atleast 1.3 repeating units derived from thehydroxymethyl-group-containing fatty acid or ester per total number ofhydroxyl, primary amine and secondary amine groups on the initiatorcompound, and the hydroxymethyl-containing polyester polyol has anequivalent weight of at least 400 up to 15,000. Preferred such polyolshave the following average structure:[H—X]_((n-p))—R—[X—Z]_(p)  (V)wherein R is the residue of an initiator compound having n hydroxyland/or primary or secondary amine groups, where n is at least two; eachX is independently —O—, —NH— or —NR′— in which R′ is an inertlysubstituted alkyl, aryl, cycloalkyl, or aralkyl group, p is a numberfrom 1 to n representing the average number of [X—Z] groups perhydroxymethyl-containing polyester polyol molecule, Z is a linear orbranched chain containing one or more A groups, provided that theaverage number of A groups per molecule is ≧1.3 times n, and each A isindependently selected from the group consisting of A1, A2, A3, A4 andA5, provided that at least some A groups are A1, A2 or A3, wherein A1is:

wherein B is H or a covalent bond to a carbonyl carbon atom of another Agroup; m is number greater than 3, n is greater than or equal to zeroand m+n is from 11 to 19; A2 is:

wherein B is as before, v is a number greater than 3, r and s are eachnumbers greater than or equal to zero with v+r+s being from 10 to 18, A3is:

wherein B, v, each r and s are as defined before, t is a number greaterthan or equal to zero, and the sum of v, r, s and t is from 10 to 18; A4is

where w is from 10-24, and A5 is

where R′ is a linear or branched alkyl group that is substituted with atleast one cyclic ether group and optionally one or more hydroxyl groupsor other ether groups.

3. An amide group-containing polyol as described in WO 2007/019063.Among these are amide compounds having hydroxymethyl groups, which areconveniently described as an amide of (1) a primary or secondary aminecompound that contains at least one hydroxyl group with (2) a fatty acidthat contains at least one hydroxymethyl group. This type of amide hasat least one hydroxyl-substituted organic group bonded to the amidenitrogen. A C₇₋₂₃ hydrocarbon group is bonded to the carbonyl carbon ofthe amide group. The C₇₋₂₃ hydrocarbon group is itself substituted withat least one hydroxymethyl group. Other amide group-containing polyolsare conveniently described as an amide of a fatty acid (or ester) and ahydroxyl-containing primary or secondary amine, in which the fatty acidgroup has been modified to introduce one or more(N-hydroxyalkyl)aminoalkyl groups.

4. A hydroxyl ester-substituted fatty acid ester as described in WO2007/019051. The materials contain at least two different types of estergroups. One type of ester group corresponds to the reaction product ofthe carboxylic acid group of a fatty acid with a compound having two ormore hydroxyl groups. The second type of ester group is pendant from thefatty acid chain, being bonded to the fatty acid chain through the —O—atom of the ester group. The pendant ester group is conveniently formedby epoxidizing the fatty acid (at the site of carbon-carbon unsaturationin the fatty acid chain), followed by reaction with a hydroxy acid orhydroxy acid precursor. The pendant ester group includes at least onefree hydroxyl group. These materials can be represented by the structure[HO]_((p-x))—R—[O—C(O)—R¹]_(x)  (XI)wherein R represents the residue, after removal of hydroxyl groups, of acompound having p hydroxyl groups, R¹ represents the hydrocarbon portionof a fatty acid, and x is a number from 1 to p. p is 2 or more, asdiscussed before. Each —R—O—C(O)— linkage represents an ester group ofthe first type discussed above. At least a portion of the R¹ chains aresubstituted with at least one hydroxyl-containing ester group, which canbe represented as—O—C(O)—R²—OH_(y)  (XII)wherein R² is a hydrocarbyl group that may be inertly substituted, and yis 1 or more, preferably 1 or 2. The bond shown at the left of thestructure attaches to a carbon atom of the fatty acid chain. Inertsubstituents in this context are those which do not interfere with theformation of the material or its use in making a polyurethane.

5. A “blown” soybean oil as described in US Published PatentApplications 2002/0121328, 2002/0119321 and 2002/0090488.

6. An oligomerized vegetable oil or animal fat as described in WO06/116456. The oil or fat is oligomerized by epoxidizing some or all ofthe carbon-carbon double bonds in the starting material, and thenconducting a ring-opening reaction under conditions which promoteoligomerization. Some residual epoxide groups often remain in thismaterials. A material of this type having a hydroxyl functionality ofabout 4.4 and a molecular weight of about 1100 is available from CargillInc. under the trade name BiOH.

7. Hydroxyl-containing cellulose-lignin materials.

8. Hydroxyl-containing modified starches.

In a preferred embodiment, the methylene bis(cyclohexylamine)-initiatedpolyol is used as a mixture with at least one other polyether polyolthat has an average functionality of from 4.5 to 7 hydroxyl groups permolecule and a hydroxyl equivalent weight of 100 to 175. The otherpolyether polyol may be, for example, a sorbitol- orsucrose/glycerine-initiated polyether. The methylenebis(cyclohexylamine)-initiated polyol may constitute from 10 to 70% ofthe weight of the mixture in this case. Examples of suitable sorbitol-or sucrose/glycerine-initiated polyethers that can be used includeVoranol® 360, Voranol® RN411, Voranol® RN490, Voranol® 370, Voranol®446, Voranol® 520, Voranol® 550 and Voranol® 482 polyols, all availablefrom Dow Chemical.

In another preferred embodiment, the methylenebis(cyclohexylamine)-initiated polyol is used in a polyol mixture thatalso contains at least one other polyether polyol that has an averagefunctionality of from 4.5 to 7 hydroxyl groups per molecule and ahydroxyl equivalent weight of 100 to 175, and which is notamine-initiated, and at least one other amine-initiated polyol having anaverage functionality of from 2.0 to 4.0 (preferably 3.0 to 4.0) and ahydroxyl equivalent weight of from 100 to 225. The other amine-initiatedpolyol may be initiated with, for example, ammonia, ethylene diamine,hexamethylenediamine, diethanolamine, monoethanolamine,N-methyldiethanolamine, piperazine, aminoethylpiperazine,diisopropanolamine, monoisopropanolamine, methanolamine,dimethanolamine, toluene diamine (all isomers) and the like. Ethylenediamine- and toluene diamine-initiated polyols are preferred in thiscase. The polyol mixture may contain from 5 to 50% by weight of themethylene bis(cyclohexylamine)-initiated polyol, from 20 to 70% byweight of the non-amine-initiated polyol and from 2 to 20% by weight ofthe other amine-initiated polyol. The polyol mixture may contain up to15% by weight of still another polyol, which is not amine-initiated andwhich has a hydroxyl functionality of 2.0 to 3.0 and a hydroxylequivalent weight of from 90 to 500, preferably from 200 to 500.Specific examples of polyol mixtures as just described include a mixtureof from 5 to 50% by weight of the methylenebis(cyclohexylamine)-initiated polyol, from 20 to 70% of a sorbitol orsucrose/glycerine initiated polyether polyol having an averagefunctionality of from 4.5 to 7 hydroxyl groups per molecule and ahydroxyl equivalent weight of 100 to 175, from 2 to 20% by weight of anethylenediamine-initiated polyol having an equivalent weight of from 100to 225, and from 0 to 15% by weight of a non-amine-initiated polyolhaving a functionality of from 2.0 to 3.0 and hydroxyl equivalent weightof from 200 to 500.

Polyol mixtures as described can be prepared by making the constituentpolyols individually, and then blending them together. Alternatively,polyol mixtures can be prepared by forming a mixture of the respectiveinitiator compounds, and then alkoxylating the initiator mixture to formthe polyol mixture directly. Combinations of these approaches can alsobe used.

The polyurethane-forming composition contains at least one organicpolyisocyanate. The organic polyisocyanate or mixture thereofadvantageously contains an average of at least 2.5 isocyanate groups permolecule. A preferred isocyanate functionality is from about 2.5 toabout 3.6 or from about 2.6 to about 3.3 isocyanate groups/molecule. Thepolyisocyanate or mixture thereof advantageously has an isocyanateequivalent weight of from about 130 to 200. This is preferably from 130to 185 and more preferably from 130 to 170. These functionality andequivalent weight values need not apply with respect to any singlepolyisocyanate in a mixture, provided that the mixture as a whole meetsthese values.

Suitable polyisocyanates include aromatic, aliphatic and cycloaliphaticpolyisocyanates. Aromatic polyisocyanates are generally preferred.Exemplary polyisocyanates include, for example, m-phenylenediisocyanate, 2,4- and/or 2,6-toluene diisocyanate (TDI), the variousisomers of diphenylmethanediisocyanate (MDI),hexamethylene-1,6-diisocyanate, tetramethylene-1,4-diisocyanate,cyclohexane-1,4-diisocyanate, hexahydrotoluene diisocyanate,hydrogenated MDI (H₁₂ MDI), naphthylene-1,5-diisocyanate,methoxyphenyl-2,4-diisocyanate, 4,4′-biphenylene diisocyanate,3,3′-dimethoxy-4,4′-biphenyl diisocyanate,3,3′-dimethyldiphenylmethane-4,4′-diisocyanate, 4,4′,4″-triphenylmethanediisocyanate, polymethylene polyphenylisocyanates, hydrogenatedpolymethylene polyphenyl polyisocyanates, toluene-2,4,6-triisocyanateand 4,4′-dimethyldiphenylmethane-2,2′,5,5′-tetraisocyanate. Preferredpolyisocyanates are the so-called polymeric MDI products, which are amixture of polymethylene polyphenylene polyisocyanates in monomeric MDI.Especially suitable polymeric MDI products have a free MDI content offrom 5 to 50% by weight, more preferably 10 to 40% by weight. Suchpolymeric MDI products are available from The Dow Chemical Company underthe trade names PAPI® and Voranate®.

An especially preferred polyisocyanate is a polymeric MDI product havingan average isocyanate functionality of from 2.6 to 3.3 isocyanategroups/molecule and an isocyanate equivalent weight of from 130 to 170.Suitable commercially available products of that type include PAPI® 27,Voranate™ M229, Voranate™ 220, Voranate™ 290, Voranate™ M595 andVoranate™ M600, all from Dow Chemical.

Isocyanate-terminated prepolymers and quasi-prepolymers (mixtures ofprepolymers with unreacted polyisocyanate compounds) can also be used.These are prepared by reacting a stoichiometric excess of an organicpolyisocyanate with a polyol, such as the polyols described above.Suitable methods for preparing these prepolymers are well known. Such aprepolymer or quasi-prepolymer preferably has an isocyanatefunctionality of from 2.5 to 3.6 and an isocyanate equivalent weight offrom 130 to 200.

The polyisocyanate is used in an amount sufficient to provide anisocyanate index of from 80 to 600. Isocyanate index is calculated asthe number of reactive isocyanate groups provided by the polyisocyanatecomponent divided by the number of isocyanate-reactive groups in thepolyurethane-forming composition (including those contained byisocyanate-reactive blowing agents such as water) and multiplying by100. Water is considered to have two isocyanate-reactive groups permolecule for purposes of calculating isocyanate index. A preferredisocyanate index is from 90 to 400 and a more preferred isocyanate indexis from 100 to 150.

The blowing agent used in the polyurethane-forming composition includesat least one physical blowing agent which is a hydrocarbon,hydrofluorocarbon, hydrochlorofluorocarbon, fluorocarbon, dialkyl etheror a fluorine-substituted dialkyl ether, or a mixture of two or morethereof. Blowing agents of these types include propane, isopentane,n-pentane, n-butane, isobutane, isobutene, cyclopentane, dimethyl ether,1,1-dichloro-1-fluoroethane (HCFC-141b), chlorodifluoromethane(HCFC-22), 1-chloro-1,1-difluoroethane (HCFC-142b),1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,1,3,3-pentafluorobutane(HFC-365mfc), 1,1-difluoroethane (HFC-152a),1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) and1,1,1,3,3-pentafluoropropane (HFC-245fa). The hydrocarbon andhydrofluorocarbon blowing agents are preferred. It is generallypreferred to further include water in the formulation, in addition tothe physical blowing agent.

Blowing agent(s) are preferably used in an amount sufficient such thatthe formulation cures to form a foam having a molded density of from 16to 160 kg/m³, preferably from 16 to 64 kg/m³ and especially from 20 to48 kg/m³. To achieve these densities, the hydrocarbon orhydrofluorocarbon blowing agent conveniently is used in an amountranging from about 10 to about 40, preferably from about 12 to about 35,parts by weight per 100 parts by weight polyol(s). Water reacts withisocyanate groups to produce carbon dioxide, which acts as an expandinggas. Water is suitably used in an amount within the range of 0.5 to 3.5,preferably from 1.5 to 3.0 parts by weight per 100 parts by weight ofpolyol(s).

The polyurethane-forming composition typically will include at least onecatalyst for the reaction of the polyol(s) and/or water with thepolyisocyanate. Suitable urethane-forming catalysts include thosedescribed by U.S. Pat. No. 4,390,645 and in WO 02/079340, bothincorporated herein by reference. Representative catalysts includetertiary amine and phosphine compounds, chelates of various metals,acidic metal salts of strong acids; strong bases, alcoholates andphenolates of various metals, salts of organic acids with a variety ofmetals, organometallic derivatives of tetravalent tin, trivalent andpentavalent As, Sb and Bi and metal carbonyls of iron and cobalt.

Tertiary amine catalysts are generally preferred. Among the tertiaryamine catalysts are dimethylbenzylamine (such as Desmorapid® DB fromRhine Chemie), 1,8-diaza (5,4,0)undecane-7 (such as Polycat® SA-1 fromAir Products), pentamethyldiethylenetriamine (such as Polycat® 5 fromAir Products), dimethylcyclohexylamine (such as Polycat® 8 from AirProducts), triethylene diamine (such as Dabco® 33LV from Air Products),dimethyl ethyl amine, n-ethyl morpholine, N-alkyl dimethylaminecompounds such as N-ethyl N,N-dimethyl amine and N-cetylN,N-dimethylamine, N-alkyl morpholine compounds such as N-ethylmorpholine and N-coco morpholine, and the like. Other tertiary aminecatalysts that are useful include those sold by Air Products under thetrade names Dabco® NE1060, Dabco® NE1070, Dabco®NE500, Dabco® TMR-2,Dabco® TMR 30, Polycat® 1058, Polycat® 11, Polycat 15, Polycat® 33Polycat® 41 and Dabco® MD45, and those sold by Huntsman under the tradenames ZR 50 and ZR 70. In addition, certain amine-initiated polyols canbe used herein as catalyst materials, including those described in WO01/58976 A. Mixtures of two or more of the foregoing can be used.

The catalyst is used in catalytically sufficient amounts. For thepreferred tertiary amine catalysts, a suitable amount of the catalystsis from about 1 to about 4 parts, especially from about 1.5 to about 3parts, of tertiary amine catalyst(s) per 100 parts by weight of thepolyol(s).

The polyurethane-forming composition also preferably contains at leastone surfactant, which helps to stabilize the cells of the composition asgas evolves to form bubbles and expand the foam. Examples of suitablesurfactants include alkali metal and amine salts of fatty acids such assodium oleate, sodium stearate sodium ricinolates, diethanolamineoleate, diethanolamine stearate, diethanolamine ricinoleate, and thelike: alkali metal and amine salts of sulfonic acids such asdodecylbenzenesulfonic acid and dinaphthylmethanedisulfonic acid;ricinoleic acid; siloxane-oxyalkylene polymers or copolymers and otherorganopolysiloxanes; oxyethylated alkylphenols (such as Tergitol NP9 andTriton X100, from The Dow Chemical Company); oxyethylated fatty alcoholssuch as Tergitol 15-S-9, from The Dow Chemical Company; paraffin oils;castor oil; ricinoleic acid esters; turkey red oil; peanut oil;paraffins; fatty alcohols; dimethyl polysiloxanes and oligomericacrylates with polyoxyalkylene and fluoroalkane side groups. Thesesurfactants are generally used in amount of 0.01 to 6 parts by weightbased on 100 parts by weight of the polyol.

Organosilicone surfactants are generally preferred types. A wide varietyof these organosilicone surfactants are commercially available,including those sold by Goldschmidt under the Tegostab® name (such asTegostab B-8462, B8427, B8433 and B-8404 surfactants), those sold by OSiSpecialties under the Niax® name (such as Niax® L6900 and L6988surfactants) as well as various surfactant products commerciallyavailable from Air Products and Chemicals, such as DC-193, DC-198,DC-5000, DC-5043 and DC-5098 surfactants.

In addition to the foregoing ingredients, the polyurethane-formingcomposition may include various auxiliary components such as fillers,colorants, odor masks, flame retardants, biocides, antioxidants, UVstabilizers, antistatic agents, viscosity modifiers and the like.

Examples of suitable flame retardants include phosphorus compounds,halogen-containing compounds and melamine.

Examples of fillers and pigments include calcium carbonate, titaniumdioxide, iron oxide, chromium oxide, azo/diazo dyes, phthalocyanines,dioxazines, recycled rigid polyurethane foam and carbon black.

Examples of UV stabilizers include hydroxybenzotriazoles, zinc dibutylthiocarbamate, 2,6-ditertiarybutyl catechol, hydroxybenzophenones,hindered amines and phosphites.

Except for fillers, the foregoing additives are generally used in smallamounts. Each may constitute from 0.01 percent to 3 percent of the totalweight of the polyurethane formulation. Fillers may be used inquantities as high as 50% of the total weight of the polyurethaneformulation.

The polyurethane-forming composition is prepared by bringing the variouscomponents together under conditions such that the polyol(s) andisocyanate(s) react, the blowing agent generates a gas, and thecomposition expands and cures. All components (or any sub-combinationthereof) except the polyisocyanate can be pre-blended into a formulatedpolyol composition if desired, which is then mixed with thepolyisocyanate when the foam is to be prepared. The components may bepreheated if desired, but this is usually not necessary, and thecomponents can be brought together at about room temperature (˜22° C.)to conduct the reaction. It is usually not necessary to apply heat tothe composition to drive the cure, but this may be done if desired, too.

The invention is particularly useful in so-called “pour-in-place”applications, in which the polyurethane-forming composition is dispensedinto a cavity and foams within the cavity to fill it and providestructural and/or thermal insulative attributes to an assembly. Thenomenclature “pour-in-place” refers to the fact that the foam is createdat the location where it is needed, rather than being created in onestep and later assembled into place in a separate manufacturing step.Pour-in-place processes are commonly used to make appliance productssuch as refrigerators, freezers, and coolers and similar products whichhave walls that contain thermal insulation foam. The presence of theamine-initiated polyol in the polyurethane-forming composition tends toprovide the formulation with good flow and short demold times, while atthe same time producing a low k-factor foam.

The walls of appliances such as refrigerators, freezers and coolers aremost conveniently insulated in accordance with the invention by firstassembling an outer shell and an interior liner together, such that acavity is formed between the shell and liner. The cavity defines thespace to be insulated as well as the dimensions and shape of the foamthat is produced. Typically, the shell and liner are bonded together insome way, such as by welding, melt-bonding or through use of someadhesive (or some combination of these) prior to introduction of thefoam formulation. In most cases, the shell and liner may be supported orheld in the correct relative positions using a jig or other apparatus.One or more inlets to the cavity are provided, through which the foamformulation can be introduced. Usually, one or more outlets are providedto allow air in the cavity to escape as the cavity is filled with thefoam formulation and the foam formulation expands.

The materials of construction of the shell and liner are notparticularly critical, provided that they can withstand the conditionsof the curing and expansion reactions of the foam formulation. In mostcases, the materials of construction will be selected with regard tospecific performance attributes that are desired in the final product.Metals such as steel are commonly used as the shell, particularly inlarger appliances such as freezers or refrigerators. Plastics such aspolycarbonates, polypropylene, polyethylene styrene-acrylonitrileresins, acrylonitrile-butadiene-styrene resins or high-impactpolystyrene are used more often in smaller appliances (such as coolers)or those in which low weight is important. The liner may be a metal, butis more typically a plastic as just described.

The foam formulation is then introduced into the cavity. The variouscomponents of the foam formulation are mixed together and the mixtureintroduced quickly into the cavity, where the components react andexpand. It is common to pre-mix the polyol(s) together with the waterand blowing agent (and often catalyst and/or surfactant as well) toproduce a formulated polyol. The formulated polyol can be stored untilit is time to prepare the foam, at which time it is mixed with thepolyisocyanate and introduced into the cavity. It is usually notrequired to heat the components prior to introducing them into thecavity, nor it is usually required to heat the formulation within thecavity to drive the cure, although either or both of these steps may betaken if desired. The shell and liner may act as a heat sink in somecases, and remove heat from the reacting foam formulation. If necessary,the shell and/or liner can be heated somewhat (such as up to 50° C. andmore typically 35-40° C.) to reduce this heat sink effect, or to drivethe cure.

Enough of the foam formulation is introduced such that, after it hasexpanded, the resulting foam fills those portions of the cavity wherefoam is desired. Most typically, essentially the entire cavity is filledwith foam. It is generally preferred to “overpack” the cavity slightly,by introducing more of the foam formulation than is minimally needed tofill the cavity, thereby increasing the foam density slightly. Theoverpacking provides benefits such as better dimensional stability ofthe foam, especially in the period following demold. Generally, thecavity is overpacked by from 4 to 20% by weight. The final foam densityfor most appliance applications is preferably in the range of from 28 to40 kg/m³.

After the foam formulation has expanded and cured enough to bedimensionally stable, the resulting assembly can be “demolded” byremoving it from the jig or other support that is used to maintain theshell and liner in their correct relative positions. Short demold timesare important to the appliance industry, as shorter demold times allowmore parts to be made per unit time on a given piece of manufacturingequipment.

Demold times can be evaluated as follows: A 28-liter “jumbo” Brett moldcoated with release agent is conditioned to a temperature of 45° C. 896g±4 g of a foam formulation is injected into the mold in order to obtaina 32 kg/m³ density foam. After a period of 6 minutes, the foam isremoved from the mold and the thickness of the foam is measured. After afurther 24 hours, the foam thickness is re-measured. The differencebetween the thickness after 24 hours and the initial thickness is anindication of the post-demold expansion of the foam, which in turn is anindication of whether the foam is adequately cured. A post-demoldexpansion of no more than 4 mm on this test generally indicates that thefoam has cured adequately. The test can be repeated if necessary usingdifferent cure times to determine, for a specific formulation, thedemold time that is necessary to obtain adequate cure. A demold time ofno more than 6 minutes is often obtained with this invention.

As mentioned, flow is another important attribute of the foamformulation. For purposes of this invention, flow is evaluated using arectangular “Brett” mold, having dimensions of 200 cm×20 cm×5 cm(˜6′6″×8″×2″). The polyurethane-forming composition is formed, andimmediately injected into the Brett mold, which is oriented vertically(i.e., 200 cm direction oriented vertically) and preheated to 45±5° C.The composition is permitted to expand against its own weight and cureinside the mold. The amount of polyurethane-forming composition isselected such that the resulting foam just fills the mold. The densityof the resulting foam is then measured and compared with the density ofa free-rise foam made from the same formulation (by injecting theformulation into a plastic bag or open cardboard box where it can expandfreely vertically and horizontally against atmospheric pressure). Theratio of the Brett mold foam density to the free rise density isconsidered to represent the “flow index” of the formulation. With thisinvention, flow index values are typically below 1.8, and are preferablyfrom 1.2 to 1.5.

The polyurethane foam advantageously exhibits a low k-factor. Thek-factor of a foam may depend on several variables, of which density isan important one. For many applications, a rigid polyurethane foamhaving a density of from 28.8 to 40 kg/m³ (1.8 to 2.5 pounds/cubic foot)exhibits a good combination of physical properties, dimensionalstability, and cost. Foam in accordance with the invention, having adensity within that range, preferably exhibits a 10° C. k-factor of nogreater than 22, preferably no greater than 20, and more preferably nogreater than 19.5 mW/m-° K. Higher density foam may exhibit a somewhathigher k-factor.

In addition to the appliance and thermal insulation foams describedabove, the invention is also useful to produce vehicle noise dampeningfoams, one or more layers of a laminated board, pipe insulation andother foam products. The invention is of special interest when a rapidcure is wanted, and or good thermal insulating properties are wanted inthe foam.

If desired, the process of the invention can be practiced in conjunctionwith the vacuum assisted injection (VAI) methods described, for example,in WO 07/058,793, in which the reaction mixture is injected into aclosed mold cavity which is at a reduced pressure. In the VAI process,the mold pressure is reduced to 300 to 950 mbar (30-95 kPa), preferablyfrom 400 to 900 mbar (40-90 kPa) and even more preferably from 500 to850 mbar (50-85 kPa), before or immediately after the foam formingcomposition is charged to the mold. Furthermore, the packing factor(ratio of the density of the molded foam divided by its free risedensity) should be from 1.03 to 1.9.

A higher formulation viscosity is often beneficial in the VAI process,as the higher viscosity helps to prevent cells from rupturing andcollapsing until the foam formulation has cured. Therefore, a methylenebis(cyclohexylamine)-initiated polyol in accordance with the inventionthat has a viscosity of at least 10,000 cps at 50° C. is preferred. Themethylene bis(cyclohexylamine)-initiated polyol more preferably has aviscosity of at least 25,000 or at least 40,000 at 50° C. The viscosityof the methylene bis(cyclohexylamine)-initiated polyol may be as high as100,000 cps at 50° C.

The following examples are provided to illustrate the invention, but arenot intended to limit the scope thereof. All parts and percentages areby weight unless otherwise indicated.

EXAMPLE 1

28 moles of methylene bis(cyclohexylamine) are added to a reactionvessel under nitrogen. The vessel and its contents are heated to 125°C., and 85 moles of propylene oxide are fed in. The reaction mixture isallowed to digest at 125° C. for 4 hours, at which time 82 g of a 45% byweight potassium hydroxide solution is added. The water is then removedunder vacuum and 72 moles of propylene oxide are fed into the reactor.The reaction mixture is again allowed to digest for 4 hours at 125° C.,after which time an acetic acid solution is added. The product polyolhas a hydroxyl number of 415 mg KOH/g and a viscosity of 73,000 cps at50° C.

EXAMPLE 2

Rigid polyurethane foam is produced from the components described inTable 1. Foam processing is performed using a Hi Tech CS-50 highpressure machine operated at a throughput of 175-225 g/s. The foamformulation is injected into a bag (to measure free rise density) andinto a vertical Brett mold which is preheated to 45° C. Componenttemperatures prior to mixing are ˜21° C.

TABLE 1 Component Parts By Weight Sorbitol-initiated polyol¹  57.0Polyol of Example 1  15.6 Ethylene diamine-initiated polyol²  11.0Poly(propylene oxide) diol³  10.0 Water   2.4 Silicone surfactant   2.0Amine Catalysts   2.0 Cyclopentane  14.0 Polymeric MDI⁴ (index) 155 (115index) ¹A 6.0 functional poly(propylene oxide) having a hydroxyl numberof 482, commercially available as Voranol ® RN 482 polyol from DowChemical. ²An ethylene diamine-initiated poly(propylene oxide) having ahydroxyl number of 500. ³A poly(propylene oxide) diol having a molecularweight of about 400. ⁴Voranate ™ M229 polymeric MDI, available from DowChemical.

The composition has a cream time of 4 seconds, a gel time of 33 secondsand a tack-free time of 45 seconds. The free rise density is 22.24kg/m³, and the minimum fill density is 29.72 kg/m³. The flow index istherefore 1.336. The foam has an average compressive strength of 137.7kPa.

K-factor is measured on 8″×1″×1″ (20×2.5×2.5 cm) samples using a LaserComp Fox 200 device, with an upper cold plate temperature of −3° C. anda lower warm plate temperature of 23° C., and found to be 19.16 mW/m-°K.

1. A process for preparing a rigid polyurethane foam, comprising a)forming a reactive mixture consisting of 1) a polyol mixture thatcontains 5 to 50% by weight of (i) a methylenebis(cyclohexylamine)-initiated polyol having an average hydroxylfunctionality of 3.7 to 4.0 and a hydroxyl equivalent weight of from 100to 130, the methylene bis(cyclohexylamine)-initiated polyol being areaction product of ethylene oxide, propylene oxide or a mixture ofethylene oxide and propylene oxide with a methylene bis(cyclohexylamine)initiator compound, (ii) 20 to 70% of a sorbitol or sucrose andglycerine initiated polyether polyol having an average functionality of4.5 to 7 hydroxyl groups and a hydroxy equivalent weight of 100 to 175(iii) 2 to 20% by weight of an ethylenediamine-initiated polyol havingan equivalent weight of 100 to 225 and (iv) 0 to 15% by weight of anon-amine-initiated polyol having a functionality of 2.0 to 3.0 and ahydroxyl equivalent weight of 200 to 500; 2) at least one hydrocarbon,hydrofluorocarbon, hydrochlorofluorocarbon, fluorocarbon, dialkyl etheror fluorine-substituted dialkyl ether physical blowing agent; 3) water;4) at least one polyisocyanate; 5) one or more catalysts for thereaction of the polyols and water with the polyisocyanate; 6) asurfactant; and 7) optionally one or more of a filler, a colorant, anodor mask, a flame retardant, a biocide, an antioxidant, a UVstabilizer, an antistatic agent; and b) subjecting the reactive mixtureto conditions such that the reactive mixture expands and cures to form arigid polyurethane foam.
 2. The process of claim 1 wherein the methylenebis(cyclohexylamine)-initiated polyol is a reaction product of at leastone C₂-C₄ alkylene oxide with methylene bis(4-aminocyclohexane),methylene bis(2-aminocyclohexane), 2,4′-diamino methylenebis(cyclohexane), methylene bis(4-amino-2-methyl-cyclohexane), methylenebis(2-amino-4-methyl-cyclohexane), methylenebis(4-amino-3-methyl-cyclohexane) or a mixture of any two or morethereof.